1. Field of the Invention
The present invention relates to a method of manufacturing a thin film transistor (hereinafter referred to as TFT) using a single crystal silicon thin film formed on a substrate having an insulating surface, and to a method of manufacturing a semiconductor device including a semiconductor circuit constituted by TFTs.
Incidentally, in the present specification, the semiconductor device indicates any device capable of functioning by using semiconductor characteristics, and the category thereof includes an electro-optical device typified by a liquid crystal display device, a semiconductor circuit in which TFTs are integrated, and an electronic apparatus including such an electro-optical device or semiconductor circuit as a part.
2. Description of the Related Art
In recent years, VLSI techniques have been remarkably developed, and an attention has been paid to an SOI (Silicon on Insulator) structure for realizing low power consumption. This technique is such a technique that an active region (a channel formation region) of an FET, which has been conventionally formed of bulk single crystal silicon, is formed of a single crystal silicon thin film.
In an SOI substrate, a buried oxide film made of silicon oxide exists on single crystal silicon, and a single crystal silicon thin film is formed thereon. Although various methods are known as methods of manufacturing such an SOI substrate, an attention has been recently paid to a bonded SOI substrate. The bonded SOI substrate realizes the SOI structure by bonding two silicon substrates as suggested by its name. This technique has a possibility that a single crystal silicon thin film can be formed in future also on a glass substrate or the like.
Among the bonded SOI substrates, in recent years, an attention has been especially paid to a technique called Smart-Cut (registered trademark of SOITEC Co.). Smart-Cut method is a technique developed by SOITEC Co. in France in 1996, and is a method of manufacturing a bonded SOI substrate using hydrogen embrittlement. The particular technique of the Smart-Cut method is disclosed in xe2x80x9cIndustrial Research Society (Kogyo Chosa Kai); Electronic Material, August, pp. 83-87, 1977xe2x80x9d in detail.
As another method, there is known a technique called ELTRAN (trademark of Canon K. K.). This technique is a method of manufacturing an SOI substrate using selective etching of a porous silicon layer. The particular technique of ELTRAN method is disclosed in xe2x80x9cT. Yonehara, K. Sakaguchi and T. Hamaguchi: Appl. Phys. Lett. 43[3], 253 (1983)xe2x80x9d in detail.
Even if either one of the methods is used, a single crystal silicon thin film having a desired thickness can be formed on a substrate. However, in both methods, since a high temperature heat treatment is carried out in a step of bonding two substrates, there arises a problem in which intense stress is generated and remains in the formed single crystal silicon film.
If the stress at this time remains in an active layer of a TFT formed of the single crystal silicon thin film, it may function as trap levels for carriers or may become a factor to cause change in TFT characteristics with time elapses. This problem is a very important problem when Smart-Cut method or ELTRAN method is used, and a fundamental solution thereof has been required.
The present invention has been made to solve the foregoing problem, and an object of the present invention is to provide a method of removing trap levels and defects due to stress, from a single crystal silicon thin film formed by Smart-Cut method or ELTRAN method.
Another object of the present invention is to improve an operation performance of a TFT that employs such a single crystal silicon thin film, and further to improve an operation performance and reliability of a semiconductor circuit or an electro-optical device employing TFTs.
Still another object of the present invention is to improve an operation performance and reliability of an electronic equipment incorporating such a semiconductor circuit or an electro-optical device.
According to one aspect of the present invention, a method of manufacturing a semiconductor device is characterized by comprising a first step of forming a hydrogen added layer by adding hydrogen to a first single crystal silicon substrate having a silicon oxide film on a major surface, from a major surface side; a second step of bonding the first single crystal silicon substrate to a second substrate as a support through the silicon oxide film; a third step of separating the first single crystal silicon substrate by a first heat treatment; a fourth step of carrying out a second heat treatment to a single crystal silicon thin film having remained on the second substrate in the third step; a fifth step of flattening a major surface of the single crystal silicon thin film; a sixth step of forming an island-like silicon layer by patterning the single crystal silicon thin film; and a seventh step of carrying out a thermal oxidation treatment to the island-like silicon layer.
According to another aspect of the present invention, a method of manufacturing a semiconductor device is characterized by comprising a first step of forming a hydrogen added layer by adding hydrogen to a first single crystal silicon substrate having a silicon oxide film on a major surface, from a major surface side; a second step of bonding the first single crystal silicon substrate to a second substrate as a support through the silicon oxide film; a third step of separating the first single crystal silicon substrate by a first heat treatment; a fourth step of flattening a major surface of a single crystal silicon thin film having remained on the second substrate in the third step; a fifth step of forming an island-like silicon layer by patterning the single crystal silicon thin film; and a sixth step of carrying out a thermal oxidation treatment to the island-like silicon layer.
According to still another aspect of the present invention, a method of manufacturing a semiconductor device is characterized by comprising a first step of forming a porous silicon layer by anodic oxidation of a first single crystal silicon substrate; a second step of making epitaxial growth of a single crystal silicon thin film on the porous silicon layer; a third step of forming a silicon oxide film on the single crystal silicon thin film; a fourth step of bonding the first single crystal silicon substrate to a second substrate as a support through the silicon oxide film; a fifth step of carrying out a first heat treatment to the first single crystal silicon substrate and the second substrate; a sixth step of polishing the first single crystal silicon substrate until the porous silicon layer is exposed; a seventh step of exposing the single crystal silicon thin film by removing the porous silicon layer; an eighth step of forming an island-like silicon layer by patterning the single crystal silicon thin film; and a ninth step of carrying out a thermal oxidation treatment to the island-like silicon layer.
According to still another aspect of the present invention, a method of manufacturing a semiconductor device is characterized by comprising a first step of forming a porous silicon layer by anodic oxidation of a first single crystal silicon substrate; a second step of making epitaxial growth of a single crystal silicon thin film on the porous silicon layer; a third step of forming a silicon oxide film on the single crystal silicon thin film; a fourth step of bonding the first single crystal silicon substrate to a second substrate as a support through the silicon oxide film; a fifth step of polishing the first single crystal silicon substrate until the porous silicon layer is exposed; a sixth step of exposing the single crystal silicon thin film by removing the porous silicon layer; a seventh step of forming an island-like silicon layer by patterning the single crystal silicon thin film; and an eighth step of carrying out a thermal oxidation treatment to the island-like silicon layer.
The thermal oxidation treatment is carried out at a temperature in a range of from 1050 to 1150xc2x0 C. (typically 1100xc2x0 C.). When the temperature exceeds about 1100xc2x0 C., the stress relaxation of Sixe2x80x94Oxe2x80x94Si bond occurs and the bonded interface is stabilized.
In addition, in the structure described above, it is preferable that the thermal oxidation treatment is carried out in an oxidizing atmosphere containing a halogen element. As the oxidizing atmosphere containing the halogen element, it is appropriate that a mixture gas of oxygen and hydrogen chloride (HCl) or a mixture gas of oxygen and nitrogen trifluoride (NF3) is used.
Of course, as other methods, dry O2 oxidation, wet O2 oxidation, steam (water vapor) oxidation, pyrogenic oxidation (hydrogen burning oxidation), oxygen partial pressure oxidation, or the like may also be used.
The present invention has the structure as described above. However, the most important gist of the invention is to carry out the heat treatment step at a high temperature to the island-like silicon layer made of the single crystal silicon thin film formed by using Smart-Cut method or ELTRAN method. By this, the stress within the single crystal silicon layer is relaxed, and trap levels and defects caused by stress distortions can be removed from an active layer of a TFT.
Thus, it becomes possible to restore the crystallinity of a final active layer to almost the original state of the single crystal, and to improve the operation performance and reliability of a TFT. Further, it becomes possible to improve the operation performance and reliability of any semiconductor device in which a semiconductor circuit is constituted by TFTs.